This project is directed towards an investigation of various factors involved in the control of steroid hormone synthesis in the different zones of the adrenal cortex. The mechanism of action of ACTH is being studied in several projects. A major effort is directed towards evaluating the role of protein phosphorylation/dephosphorylation as it might relate to ACTH action. This is part of a quest to attempt to identify the "rapidly-turning-over" protein hypothesized to be involved in ACTH action based on inhibition of the latter by protein synthesis inhibitors. Another project addresses the mechanism of action of ACTH in a cortisol secretor, the guinea pig. Methods being used here include the isolation of cells from zona fasciculata tissue and measurement of cholesterol side chain cleavage following exposure of cells to ACTH, cyclic nucleotides and various protein synthesis inhibitors. Evidence has been obtained for another peptide derived from pro ACTH/endorphin being involved in the control of steroidogenesis in the adrenal cortex. Studies include the analysis of the mechanism by which this peptide synergizes with ACTH and quantitation of the peptide in plasma. This peptide contains the gamma-MSH sequence in the N-terminal portion of pro ACTH/endorphin and using an antibody directed against gamma-MSH, plasma is being fractionated to identify potential active peptides. In related studies, the effects of ACTH, potassium, sodium and angiotensin II on steroidogenesis in zona glomerulosa cells of the adrenal cortex are being examined. The effect of these agents on the early and late pathway is being investigated using methods which have been developed for examination of the specific cytochrome P450 enzymes involved.